Conventionally, a so-called thick copper substrate has attracted attention as a printed-circuit board corresponding to large current. In the thick copper substrate, a base is formed by stacking a plurality of copper layers having a thickness of, for example, 70 μm or more via insulating resin layers (for example, glass epoxy resin layers). The base is formed with a plurality of through holes, and a copper plating layer connected to the copper layers is formed on an inner wall surface of the through hole. Into the through hole, a terminal is inserted and bonded by solder filled in the through hole.
Patent Document 1: Japanese Laid-open Patent Publication No. 2009-16662
Patent Document 2: Japanese Laid-open Patent Publication No. 2007-180079
Patent Document 3: Japanese Laid-open Patent Publication No. 2006-156435
Patent Document 4: Japanese Laid-open Patent Publication No. 5-304223
In recent years, a method of fixing the terminal in the through hole of the printed-circuit board without adhering it using solder, for example, a method using a press-fit pin as the terminal is devised. In this case, the press-fit pin is inserted into and fixed to the through hole without requiring solder bonding. The press-fit pin is brought into contact with and fix to, by its mechanical resilient restoring force, a copper plating layer in the through hole into which the press-fit pin is inserted.
In the case of fixing the terminal such as a press-fit pin into the through hole of the printed-circuit board without using solder, a part of a side surface of the copper plating layer is damaged (slightly chipped away, deformed or the like) inside the through hole in inserting the press-fit pin or the like. When the copper plating layer is thin, influence due to the damage to the copper plating layer in inserting the press-fit pin or the like is big, bringing about a problem of failing to secure connection reliability of the press-fit pin or the like.
Another problem is that, in the case of using the terminal such as the press-fit pin or the like in the thick copper substrate, if the copper plating layer on the inner wall surface of the through hole is thin, cracks occur due to thermal stress in the copper plating layer, caused by a difference in coefficient of thermal expansion between the copper layer and the resin layer.
To address the above problems, a measure of forming the copper plating layer thick is conceivable. However, this measure has the following problem.
The plating method is low in accuracy of controlling the thickness of the copper plating layer and therefore has a difficulty in obtaining a hole diameter with a desired accuracy corresponding to the terminal such as the press-fit pin or the like. Further, the copper plating layer is formed from the inner wall side surface of the through hole of the thick copper substrate to parts of the front and rear surfaces of the base, so that when the copper plating layer is formed thick, the front and rear surface parts become also thick. Therefore, the patterning property of the copper plating layer decreases, resulting in difficulty in microfabrication. Besides, since the thickness of the copper plating layer is proportional to the plating treatment time, forming the copper plating layer thick leads to a significant decrease in productivity.